All birds have feathers – and only birds have feathers. In fact, some species can have over 25,000, including long flight feathers, insulating downy feathers and stiff tail feathers that act like rudders.
While they obviously facilitate flight – by forming the airfoil shape that generates lift as air flows over the wing – feathers serve a great many other roles. Birds are among the most magnificently decorated creatures on Earth and they use their handsome colours to attract mates, ward off predators and also to remain unseen by blending in with the background.
Birds display different plumage depending on their age, sex and seasonal changes. They see in colour and the plumage of a male has a dramatic effect on how attractive he is to the female, which impacts on mating success. It works both ways as the males of some species judge the health of a female by her feathers.
Most of the colours are the result of chemical pigments – eg melanin, carotenoids and porphyrins – produced in the feathers as they grow. Other colours can be caused by refraction of light due to feather structure. Spectacular colours can also be made by a combination of the two; for instance, when yellow-pigmented feathers overlay those with blue-reflecting properties, the plumage will look green.
Some birds use these colours as camouflage. Depending on the season, a bird’s hormones can instruct it to shed (moult) its old feathers and grow a new set more suited to the current environment. Birds from snowy regions may be pure white in winter, but – after a moult – often regrow brighter or patterned feathers to better match the summer environment.
Birds also moult regularly in order to renew any damaged feathers because they cannot heal themselves. A moult can be total or partial during which time the damaged feather will be replaced. However if an individual feather has fallen out altogether, it will start growing a new one straight away. Growing new feathers requires a lot of the bird’s energy, though, so a complete or partial moult will never coincide with demanding events in the year like breeding, nesting or migration.